This application claims the priority benefit of Japanese patent application No. 2000-371874, filed on Dec. 6, 2000, and entitled xe2x80x9cMethod and Device for Inspecting Microactuator.xe2x80x9d
1. Technical Field
The present invention relates to a method and a device for inspecting a microactuator used for tracking control of a magnetic head in, for example, a hard disk device, and more particularly, the present invention relates to a method and a device capable of inspecting mechanical characteristics of the microactuator by using an inexpensive measuring device.
2. Description of the Related Art
In a conventional hard disk device, a base end side of a suspension is rotatably supported such that its tip side can be freely displaced in a radial direction of a disk, the disk being a recording medium. A magnetic head for reading/writing data is attached to a tip portion of the suspension, and a swinging position of the suspension is controlled by a driving current applied to a voice coil motor so that the magnetic head can move to a position corresponding to a desired track of the disk. However, since intervals between track pitches are reduced in the hard disk device due to a larger capacity of the same, controlling the swinging position of a suspension arm alone has been becoming insufficient for tracking the magnetic head well while the disk spins. Accordingly, to align the magnetic head with the track on the disk, addition of microactuator control to swing control of the suspension has been suggested.
There are few micromachine products which have been put to practical use. For inspection of frequency-velocity characteristics of the micromachine, the majority of what has been presented so far uses expensive measuring systems at a research level, and no low-cost, highly reliable, and high-throughput measuring systems aiming at mass production have not been presented. However, possible technologies and their problems regarding methods for inspecting the frequency-velocity characteristics of a comb microactuator are as follows:
(a) A side face of the comb microactuator is irradiated by a laser beam, and velocity of the comb microactuator is measured using pitch shifting of a reflected light. In this inspecting method, an expensive measuring device such as an in-plane vibration laser Doppler velocimeter (LDV) or the like is required. Also, it is difficult to perform a parallel measurement, in which a plurality of comb microactuators are subjected to the measurement simultaneously.
(b) A high frequency of 60 MHz from a pulse generator is superposed on the drive voltage (2 kHz to 200 kHz) of the comb microactuator, and power discharged to the ground through the capacitor is measured. In this inspecting method, a high-frequency circuit becomes complex, the number of components is increased, and reliability is reduced. Also, highly accurate substrate designing is required.
(c) A vibration state of the comb microactuator captured through a microscope is subjected to image processing, and amplitude thereof is measured. Also in this inspecting method, a measuring device becomes expensive, and it is difficult to perform a parallel measurement, in which the frequency-velocity characteristics of the plurality of comb microactuators are subjected to the measurement simultaneously. Moreover, a large burden is imposed on program development.
(d) The comb microactuator receives a drive voltage to be displaced, and while being displaced, a capacity measurement is performed. In this inspecting method, since fluctuation of about 20% of a 3 pF capacity is measured, a highly accurate measuring system is necessary. The capacity measurement also takes time, and only a static state of the comb microactuator can be inspected.
Thus, it is an object of the present invention to provide a method and a device for inspecting a microactuator capable of inspecting mechanical characteristics without using an expensive device such as a laser measuring device or the like.
A microactuator inspecting method according to a first aspect of the invention is characterized in that a capacitor is provided, having both poles thereof being freely displaced relative to each other with respect to an AC drive voltage, which displaces a specified object based on relative movements of both of the poles of the capacitor. Such microactuator inspecting method comprises the steps of: supplying the AC drive voltage to the capacitor while changing a frequency thereof within a specified range; detecting a current value regarding a specified harmonic content with respect to each frequency of the AC drive voltage from a current of the capacitor; detecting a relation between a frequency fa and a current value I of the specified harmonic content as a first electric characteristic fa-I of the microactuator; and determining whether a mechanical characteristic of the microactuator is good or bad based on the first electric characteristic fa-I of the microactuator.
A range in which the frequency of the AC drive voltage supplied to the capacitor of the microactuator changes is, for example, from 1 kHz to 40 kHz, and generally in a range from 2 kHz to 20 kHz. In a typical microactuator, a plurality of capacitors are provided and are connected in parallel. Movable electrodes of all the capacitors are linked so as to be displaced integrally.
The current value of the harmonic content is detected by using, for example, a fast Fourier transformer (FFT) or the like. The FFT is not expensive, and provided for example in a general digital oscilloscope. Change in frequency includes both continuous change and discontinuous change by a specified amount when the frequency of the AC drive voltage changes within a specified range.
With regard to the capacitor used as a driving source to displace the object, a specified correspondence between the mechanical characteristic thereof and the first electric characteristic has been discovered by the inventors of the present invention, as described later. According to the first aspect of the present invention, it is possible to determine whether the mechanical characteristic of the capacitor is good or bad by investigating the first electric characteristic that can be measured using an inexpensive measuring device, instead of by inspecting the mechanical characteristic requiring the use of an expensive measuring device.
The general digital oscilloscope has a plurality of input channels. By inputting each current of the capacitor of each of a plurality of microactuators to each input channel of the digital oscilloscope, it is possible to enhance inspection efficiency by simultaneously inspecting the mechanical characteristic of the plurality of microactuators. When directly measuring the mechanical characteristic by an in-plane vibration laser Doppler velocimeter (LDV), it is difficult to simultaneously inspect the mechanical characteristic of a plurality of chips of microactuators arrayed in a grid form.
The microactuator inspecting method according to a second aspect of the present invention is characterized in that, in the microactuator inspecting method of the first aspect, the specified harmonic content is a second harmonic content.
The microactuator inspecting method according to a third aspect of the present invention is characterized in that, in the microactuator inspecting method of the first or the second aspect in the first electric characteristic fa-I, the frequency fa is converted into a frequency fb by faxc2x7(1/a multiple of a harmonic), a second electric characteristic fb-I is detected at the same time with a current value of each fb regarded as a current value I of the fa corresponding to the fb, and whether a mechanical characteristic of the microactuator is good or bad is determined based on the second electric characteristic fb-I.
The multiple of the harmonic means a frequency of a harmonic or of a frequency of a fundamental wave. For example, if the fundamental wave is 2 kHz and the second harmonic is selected as a harmonic, the multiple of the harmonic is 4 kHz/2 kHz=2. Thus, if the specified harmonic content is the second harmonic, fb=fa/2 is established, fb being the frequency of the fundamental wave.
A frequency for the mechanical characteristic is usually related not to the harmonic but to the fundamental wave frequency. By determining whether the mechanical characteristic of the microactuator is good or bad based on the second electric characteristic f2-I, the correspondence with the mechanical characteristic of the capacitor becomes clearer.
The microactuator inspecting method according to a fourth aspect of the present invention is characterized in that, in the microactuator inspecting method of any one of the first to the third aspects, the mechanical characteristic is a frequency-velocity characteristic.
The microactuator inspecting method according to a fifth aspect of the present invention is characterized in that, in the microactuator inspecting method of any one of the first to the fourth aspects, whether the mechanical characteristic of the microactuator is good or bad is determined by comparing the mechanical characteristic corresponding to the first electric characteristic fa-I with a reference mechanical characteristic of the microactuator.
In the comparison between the mechanical characteristic corresponding to the first electric characteristic fa-I and the reference mechanical characteristic of the microactuator, a velocity peak value, a frequency at the velocity peak value, shapes of both sides of a peak in a characteristic line and the like are selected to be compared, for example, and whether the mechanical characteristic of each microactuator is good or bad is determined based on the above selected items.
The microactuator inspecting method according to a sixth aspect of the present invention is characterized in that, in the microactuator inspecting method of any one of the first to the fifth aspects, the microactuator includes a substrate, a stage rotatably supported on the substrate, and a plurality of capacitors disposed at appropriate intervals along peripheries of the stage. Each of the capacitors includes fixed electrodes fixed to the substrate, and a movable electrode fixed to the stage, which is freely displaced relative to the fixed electrodes, and change in the AC drive voltage to the capacitor causes the stage to change a rotational position thereof with respect to the substrate. The stage should preferably freely rotate with respect to the substrate while being placed above the substrate without sliding into contact with the same.
The microactuator inspecting method according to a seventh aspect of the present invention is characterized in that, in the microactuator inspecting method of the sixth aspect, the fixed and movable electrodes have pluralities of comb-tooth portions and are disposed in a manner that own comb-tooth portion is partially inserted between two adjacent comb-tooth portions of an opposite side, and an amount of mutual insertion is changed by control of the AC drive voltage to the capacitor.
The microactuator inspecting method according to an eighth aspect of the present invention is characterized in that, in the microactuator inspecting method of the seventh aspect, each capacitor includes one movable electrode and two fixed electrodes disposed to sandwich the movable electrode from both sides of a displacing direction of the movable electrode.
The microactuator inspecting method according to a ninth aspect of the present invention is characterized in that, in the microactuator inspecting method of any one of the first to the eighth aspects, the capacitor is installed in a hard disk device, the hard disk device including: a suspension with a base end side thereof being supported to allow a tip side to freely move in a radial direction of a disk, the disk being a recording medium; a gimbal having a base end portion attached to the tip portion of the suspension; the microactuator having the substrate fixed to the tip portion of the gimbal; a slider fixed to a stage of the microactuator; and a magnetic head as the specified object to be displaced integrally with the stage.
With regard to the microactuator used for focusing control of the magnetic head in the hard disk device or the like, examples of dimensions and a capacitor capacity are as follows: a verticalxc3x97horizontal dimension of the substrate is 1.7 mmxc3x972.1 mm; a height from the lower surface of the substrate to the upper surface of the stage is 0.2 mm; and the entire capacity of the capacitors connected in parallel is in a range of 2.5 pF to 3.5 pF.
A microactuator inspecting device according to a tenth aspect of the present invention provided with a capacitor having both poles thereof being freely displaced relative to each other with respect to an AC drive voltage, which displaces a specified object based on relative movements of both of the poles of the capacitor, is characterized in that the microactuator inspecting device comprises: drive voltage supplying means for supplying the AC drive voltage to the capacitor while changing a frequency thereof within a specified range; current value detecting means for detecting a current value regarding a specified harmonic content with respect to each frequency of the AC drive voltage from a current of the capacitor; first electric characteristic detecting means for detecting a relation between a frequency fa and a current value I of the specified harmonic content as a first electric characteristic fa-I of the microactuator; and determining means for determining whether a mechanical characteristic of the microactuator is good or bad based on the first electric characteristic fa-I of the microactuator.
The microactuator inspecting device according to an eleventh aspect of the present invention is characterized in that, in the microactuator inspecting device of the tenth aspect, the specified harmonic content is a second harmonic content.
The microactuator inspecting device according to a twelfth aspect of the present invention is characterized in that, in the microactuator inspecting device of the tenth or the eleventh aspect, the microactuator inspecting device further comprises: second electric characteristic detecting means for converting the frequency fa of the first electric characteristic fa-I into a frequency fb by fa(1/a multiple of a harmonic), and at the same time, detecting a second electric characteristic fb-I with a current value of each fb regarded as a current value I of the fa corresponding to the fb. The determining means determines whether a mechanical characteristic of the microactuator is good or bad based on the second electric characteristic fb-I.
The microactuator inspecting device according to a thirteenth aspect of the present invention is characterized in that, in the microactuator inspecting device of any one of the tenth to the twelfth aspects, the mechanical characteristic is a frequency-velocity characteristic.
The microactuator inspecting device according to a fourteenth aspect of the present invention is characterized in that, in the microactuator inspecting device of any one of the tenth to the thirteenth aspects, the determining means determines whether a mechanical characteristic of the microactuator is good or bad by comparing the mechanical characteristic corresponding to the first electric characteristic fa-I with a reference mechanical characteristic for the microactuator.
The microactuator inspecting device according to a fifteenth aspect of the present invention is characterized in that, in the microactuator inspecting device of any one of the tenth to the fourteenth aspects, the microactuator includes a substrate, a stage rotatably supported on the substrate, and a plurality of capacitors disposed at appropriate intervals along peripheries of the stage. Each of the capacitors includes fixed electrodes fixed to the substrate, and a movable electrode fixed to the stage, which is freely displaced relative to the fixed electrodes. Also, change in the AC drive voltage to the capacitor causes the stage to change a rotational position thereof with respect to the substrate.
The microactuator inspecting device according to a sixteenth aspect of the present invention is characterized in that, in the microactuator inspecting device of the fifteenth aspect, the fixed and movable electrodes have pluralities of comb-tooth portions, and are disposed in a manner that each comb-tooth portion is partially inserted between two adjacent comb-tooth portions of an opposite side, and an amount of mutual insertion is changed by control of the AC drive voltage to the capacitor.
The microactuator inspecting device according to a seventeenth aspect of the present invention is characterized in that, in the microactuator inspecting device of the sixteenth aspect, each capacitor includes one movable electrode and two fixed electrodes disposed to sandwich the movable electrode from both sides of a displacing direction of the movable electrode.
The microactuator inspecting device according to an eighteenth aspect of the present invention is characterized in that, in the microactuator inspecting device of any one of the tenth to the seventeenth aspects, the capacitor is installed in a hard disk device, the hard disk device including: a suspension with a base end side thereof being supported to allow a tip side to freely move in a radial direction of a disk, the disk being a recording medium; a gimbal having a base end portion attached to the tip portion of the suspension; the microactuator having the substrate fixed to the tip portion of the gimbal; a slider fixed to a stage of the microactuator; and a magnetic head as the specified object to be integrally displaced with the stage.